Phase locking and AC amplification of small Josephson junctions

We have addressed the problem of the phase-locking mechanism of a single Josephson junction irradiated with microwaves, and have numerically and theoretically explored the possibility to achieve ac gain in this system. By investigating the capability of Josephson junctions to enhance the signal received form an external rf source we obtain useful information of the possibility of mutual phase-locking of large arrays of junctions.